Flowsheet development for the selective flotation of lepidolite from the Beauvoir granite from mineralogical insights

Abstract

This paper presents the results of a preliminary study aiming at developing a flowsheet to recover lithium hosted in lepidolite and potential metallic by-products from the Beauvoir rare metal granite (Allier, France). One of the main challenges with such unconventional lithium deposits is the different liberation mesh sizes between the coarse-grained lepidolite (∼300 µm) and the finer-grained (∼100 µm) by-products bearing minerals, namely cassiterite (Sn), columbite (Nb), tantalite and microlite (Ta). A beneficiation flowsheet starting by lepidolite flotation was developed, followed by gravity concentration through Falcon centrifugal separation to recover all by-products in a bulk heavy-minerals concentrate. All by-products behaviours were followed using the most enriched one in the granite, namely cassiterite. To reach an optimal liberation of lepidolite, a theoretical mesh was estimated, both based on grain size distribution (GSD) calculated on thin sections and on automated mineralogy carried out on samples grounded at distinct top sizes (−500 µm, −355 µm, − 250 µm and −177 µm). Results suggest that lepidolite can be effectively recovered using froth flotation with 78 % of lepidolite recovered with a concentrate containing 50 % of lepidolite. However, while most by-products bearing minerals report to the tailings during this flotation step, half of the cassiterite is recovered in the lepidolite concentrate for the finest size ranges (10–177 µm). Such an issue likely stems from the significant mineral association between lepidolite and cassiterite identified in this study trough SEM and automated mineralogy methods. Therefore, these results suggest that, to optimize cassiterite and other by-products recovery from lepidolite-bearing rare metal granites, gravity concentration should be conducted first, with an intermediate feed size range (here −280 or −300 µm) to ensure the liberation of lepidolite while improving the recovery of all by-products.